Bulk products such as stone, coal, and grain, are often shipped in hopper cars that have sloping floors to allow the commodity to be discharged through hinged doors in the bottom of the car. There has been a constant problem with the incomplete unloading of such hopper cars due to friction between the commodity in the container surface and/or cohesion between the commodity and the container surface, the latter often being caused by freezing. This incomplete unloading is a particular problem in the coal industry. Coal carry back--coal retained in the hopper cars after unloading--presents a two-pronged productivity challenge because it results in both an increase in the number of hopper cars needed to deliver a given-amount of coal and an increase in the fuel costs for the "dead head" return trip of the "empty" hopper car to the source of the coal. Further, various manual methods used to assist the discharge of coal through the hopper increase the time required for unloading the car.
Various attempts have been made to provide hopper cars with coating to facilitate the unloading. For example, U.S. Pat. No. 4,425,381 to Walsh discloses applying a coating to the inside of the hopper car comprising a dispersion of waxy, short-chain telomers in a dispersing solvent. The coating is applied by spraying the inside of the hopper car shortly before or continuously during loading, with the container wall and the cargo itself receiving a thin film of the release agent. This film is worn away and needs to be reapplied each time the container is reloaded.
U.S. Pat. No. 4,410,599 to Roe et al. discloses a freeze-adherence suppression agent to prevent bulk cargo from freezing to the sides of the container. The release agent is formulated by adding polymeric ethylene oxide to a brine. This was found to reduce the freeze adherence of cargos having appreciable quantities of unwanted moisture. The release agent forms a gel at temperatures less than 65.degree. F. on the surfaces of the bin. The gel converts to a sol or colloidal fluid at temperatures above 70-80.degree. F. which can be readily hosed off the walls of the container. This release agent would also need to be reapplied frequently to the surfaces of the hopper or bin.
Accordingly, it is an object of the present invention to provide a method for treating the interior of hopper cars with a coating that helps to insure a more complete discharge of the commodity stored within the hopper.
It is a related object to provide the coating for performing the method.
It is still a further object to provide both a method and a coating that results in a durable, long lasting coating.
These objects, as well as others, are provided by a method of treating the interior of a hopper car including the application of a coating of a mixture comprising pigments including graphite, solvents, resins, a carboxylate-based drier system, and a rheological system.